1. Field of the Invention
This invention relates to a carrier for tubular articles, and more particularly to a carrier for gripping and transporting tubular preforms of thermoplastic material from which bottles or jars are formed by a blowing process. The carrier is adapted to carry heated bottle preforms between a heating station and a bottle blowing station in a reheat-blow-type blow molding machine.
2. Description of the Related Art
In apparatus for making bottles and jars by the extrusion-blow molding technique, typically a soft tubular parison that is open at both ends is transported from an extruder to a two-piece mold to be blown to expand to the interior size of the mold, cooled, and then trimmed of excess material. The neck area of the bottle or jar is formed simultaneously with the body while the parison is within the mold. In reheat and blow apparatus, a preform is injection molded to provide a tubular structure that is open at one end and closed at the other end, similar to a test tube. The neck portion, referred to as the finish, is completely formed during the injection molding process, and the preforms can be cooled and stored for later use. When a bottle is to be formed, the body of the preform is reheated in a suitable heating device, and the heated preform is thereafter carried to and placed in a bottle mold with the neck or finish extending outwardly of the mold. Pressurized air is then introduced into the preform through the neck to expand the preform body against the mold walls to form the desired bottle or jar.
Transportation of heated preforms is often carried out by employing a pallet that includes several preform holders to hold the preforms at their neck or finish area and then to carry them to the blow molding station. Some machines are arranged to carry the preforms in an inverted condition, with the open end of the preform facing in a downward direction. Other machines carry the preforms in an upright condition, with the open end facing upwardly.
When handling upright preforms, it is easier to grip the preforms internally, at the interior of the neck, rather than exteriorly, because the threads make it difficult to securely grip the outer portion of the neck without thread damage, and they also make it difficult to obtain a tight seal between the carrying device and the threads, to prevent loss of blowing pressure during the blowing operation.
One form of preform carrier for transporting tubular preforms in an upright condition by supporting the preform at the interior surface of the neck is shown in U.S. Pat. No. 4,678,425, which is owned by the assignee of the present application. The preform carrier disclosed in that patent is referred to as a spindle nose, and is in the form of an annular sleeve of plastic material that is flexible to provide a seal between it and the preform. Although that type of carrier is quite satisfactory for general use, it has been found that when wide mouth bottles or jars are to be blown, the greater variation in the size of the inner diameter of the preforms, resulting from the normal manufacturing tolerances, and the limited flexibility of a large diameter annular sleeve of the configuration shown in the patent, sometimes results in an imperfect seal between the carrier and the preform, leading to incompletely formed bottles or jars because the desired blowing pressure could not be maintained on preforms whose finish inner diameter was at or slightly above the upper tolerance limit. Additionally, upright preforms having a larger diameter finish are more difficult to carry by frictional engagement between the annular sleeve disclosed in that patent and the preform finish. There is therefore a need for an improved carrier that can simultaneously carry a wide mouth preform and also provide an adequate seal over a wide diametral tolerance range.
It is an object of the present invention to provide a preform carrier that overcomes the shortcomings of the previously-employed carriers and to avoid the problems noted above.